1. Field of the Invention
This invention relates to lined pipe joints. More particularly, the preferred embodiment of the invention relates to a pipe joint collar seal having a sealing check valve means thereon for sealing against a liner of a pipe and providing relief of pressure from outside the lining to inside The invention also relates to a pipe joint lining end which facilitates operation of the collar seal and also prevents longitudinal contraction of the pipe lining.
2. Description of the Prior Art
The concept of employing a lined pipe in an oil or gas well which is to be treated with or handle highly corrosive fluids is known. Thus, it is known to use a lined steel pipe to deliver acids and the like to a desired depth in a gas or oil well. The pipe liners may be made of plastic, stainless steel, or other corrosion resistant materials. It is also well known that such pipes or tubing involve the assembling of many shorter pipe sections wherein each pipe joint created at the junction of two pipe sections or of a pipe section and a fitting represents a potential weak point and region susceptible to acid or corrosive attack. Thus, to extend the life of the lined pipe, various gaskets or pipeline couplings have been proposed with varying degrees of success, yet none have proven to be entirely reliable. For example, the use of an internal gasket to be held under compression between the two respective pipe ends seems to be a reasonable solution. However, in practice, the repeated assembling and disassembling of the pipe under oil field conditions quickly leads to a high frequency of pipe joint failure for compressive gasket type pipe couplings Thus, the need for a reliable yet easily installed and reusable lined pipe joint, particularly for oil field applications, exists.
One solution to this problem is provided in U.S. Pat. No. 4,507,842 to Werner, assigned to the assignee of the present invention. This patent discloses an improved method for sealing and protecting a lined pipe joint which solves many problems associated with using a lined pipe within an oil or gas well in order to deliver a highly corrosive fluid to a selected subterranean strata. In this patent, a plastic collar seal is used which is placed in the interior of a pipe joint formed between first and second externally threaded lined pipe sections which are to be held together by an internally threaded pipe collar. The collar seal is a hollow, open-ended, cylindrical plastic apparatus presized to concentrically fit within the liner of the sections of lined pipe with minimum clearance. The open ends of the collar seal are internally beveled or chamfered, and the collar seal is equipped with a sealing means, such as O-rings, on each of the ends.
This prior art collar seal is further provided with an external ledge or ridge molded on the collar seal between the O-rings, and the ledge is adapted to fit within the internally threaded collar and rest on the end of one of the lined pipes The ledge is also referred to as a "no-go" ring. This ledge is positioned such that the distance from at least one end of the collar seal to the ledge exceeds the length of the unengaged portion of the threaded collar.
This apparatus has worked well, but the O-ring seals do not allow for relief of pressure from outside the liner in the event that the pipe is depressurized. That is, gas can migrate through plastic lining in the pipe causing pressure to build up and be trapped outside the lining. If the interior of the pipe is depressurized, the pressure outside of the lining can cause the lining to implode or be deformed inwardly which is an undesirable result. The O-rings seals on the prior art collar seal help keep the pressure outside the lining. The collar seal of the present invention comprises a sealing check valve means which prevents fluid pressure inside the pipe from leaking outwardly, but which will allow any pressure which accumulates outside the lining, and which enters the coupling or collar at the joint, to be relieved and flow into the interior of the pipe if the pipe is depressurized. Thus, collapse of the pipe lining in such circumstances is prevented.
Another problem which can occur in prior art plastic lined pipes is that the plastic pipe liners can shrink when exposed to high temperatures, thus resulting in the pipe liner contracting longitudinally within the pipe This can sometimes cause difficulties. For example, the prior lined pipes known to the inventor relied upon flared ends having the same thickness as the liner to anchor the liner in the pipe. When sections of such plastic lined pipe lay in the sun, they can be heated enough to cause the pipe liner to shrink and the flared ends to break. Alternate cooling and warming periods over time can then result in the unanchored pipe liner "walking out" of the metal pipe portion. When this occurs, it is virtually impossible to reposition the pipe liner properly, and so such lengths of pipe are no longer usable. Also, the flared ends of the liners of prior lined pipe are vulnerable to breakage during handling and prevent rethreading of threaded pipe, i.e., the ends must be cut off a section of pipe to rethread it and doing so cuts the flared ends off the liner, thereby eliminating the anchoring of the liner in the pipe.
The present invention solves these problems by providing a pipe lining end which is bonded to the pipe lining or integrally formed therewith and abuts grouting between the pipe lining and pipe metal outer portion. Since the grouting material does not shrink significantly relative to the outer pipe, the plastic pipe lining cannot contract longitudinally. The preferred lining end and its abutment with the grouting material are preferably much stronger than the tensile strength of the liner so that the lining end will not break if the liner tries to contract. Also, preferably, the abutment of the pipe lining end with the grout is spaced longitudinally inside the pipe from the open end of the pipe and the lining end extends from the abutment to the open end of the pipe which allows the pipe to be rethreaded Since the pipe lining cannot contract, it cannot "walk" out of the metal pipe portion or expose the ends of the outer pipe.